Terror suspect Najibullah Zazi had contacts with al Qaeda that went nearly all the way to the top — to an Osama bin Laden confidant believed to be the terrorist group’s leader in Afghanistan, US intelligence officials told The Associated Press.

Mustafa Abu al-Yazid, an Egyptian reputed to be one of the founders of the terrorist network, used a middleman to contact Zazi as the 24-year-old Afghan immigrant hatched a plot to use homemade backpack bombs, perhaps on New York’s mass transit system, the two intelligence officials said.

Al-Yazid’s contact with Zazi indicates that al Qaeda leadership took an intense interest in what US officials have called one of the most serious terrorism threats crafted on US soil since the 9/11 attacks.

“Zazi working with the al Qaeda core is exceptionally alarming,” said Daniel Bynam of the Brookings Institution’s Saban Center. “The al Qaeda core is capable of far more effective terrorist attacks than jihadist terrorists acting on their own, and coordination with the core also enables bin Laden to choose the timing to maximize the benefit to his organization.”

US intelligence officials said earlier that Zazi had contact with an unnamed senior al Qaeda operative. That helped distinguish Zazi from other would-be terrorists who have acted on their own in planning or attempting US attacks.

The officials, speaking on the condition of anonymity because the case remains under investigation, declined to describe al-Yazid’s specific interaction with Zazi, who has pleaded not guilty to conspiring to use weapons of mass destruction. But one senior US intelligence official said the contact between Zazi and the senior al Qaeda leader occurred through an intermediary.

It’s not clear if al-Yazid, an Egyptian who has worked closely with bin Laden, contacted Zazi to offer simple encouragement or help with the bombing plot prosecutors say Zazi was pursuing.

Just weeks before US intelligence officials identified Zazi as a possible terrorist threat in late August, John Brennan, President Obama’s top domestic terrorism adviser, told a Washington audience that “another attack on the US homeland remains the top priority for the al Qaeda senior leadership.”

US intelligence officials and prosecutors have said that Zazi was recruited and trained by al Qaeda. They say he and others traveled last year to Pakistan to receive the training.

Prosecutors say Zazi, during meetings with federal investigators before his arrest last month, “admitted that he received instructions from al Qaeda operatives on subjects such as weapons and explosives” during his trip to Pakistan.

Zazi, who is being held without bond while awaiting trial, has denied receiving al Qaeda training or visiting one of the group’s training camps. He said before his arrest that he traveled to Pakistan to see his wife, who lives in Peshawar.